A previously unknown work by the late author Harper Lee seems to have emerged, but it's not fiction.

Lee's feature story about a quadruple murder in Kansas was found in an FBI publication called Grapevine, the Guardian reported Monday. The murders also inspired Truman Capote's nonfiction book, "In Cold Blood," which Lee helped Capote research.

Lee biographer Charles J. Shields told the Guardian he relied on two major clues to attribute the article to Lee, who died in February at age 89. Though the piece lists no author, there's the fact that Lee helped Capote research his book and had access to information about the case that others didn't. What's more, Shields found a column in a Kansas newspaper called the Garden City Telegram announcing that Lee's article would appear in Grapevine.

Shields confirmed that the Guardian's account of his discovery is correct.

Lee's most famous work is "To Kill a Mockingbird," published in 1960, just after the newspaper column was published announcing her Grapevine article.

"Miss Harper's first novel is due for publication by Random House this spring," wrote the Garden City Telegram columnist Dolores Hope, "and advance reports say it is bound to be a success."